The project's long term objective is to develop an instrument and assay system for optical measurement of oxygen in vitro that will be used for diagnostic tests involving reactants that consume oxygen. The immediate application proposed is for cholesterol analysis using an oxidative enzyme system. The concept is that oxygen utilization is directly tied to substrate turnover, therefore, determination of the change in the amount of oxygen in a sample fluid can be an accurate measure of the substrate concentration. Preliminary results indicate that the optical sensing approach has promise and could be the basis for a system that conveniently processes multiple samples. The aim of Phase I is to thoroughly assess the range, accuracy and reliability, of the approach in order to establish its feasibility for cholesterol analysis. In this test phase, cholesterol samples of know values will be reacted with conventional enzyme reagent, and the change in oxygen content of the sample will be tracked with fiber optic oxygen sensors. The data will be compared and contrasted to the know cholesterol levels as well as the results of other conventional assay methods. The system's technology is designed to address accuracy and reliability issues in the small offices, clinics, and screening-site test settings, offering advantages over existing assay. The alternate site test market is valuable for quality health care. Cholesterol concerns are particularly important regarding coronary heart disease, and constitute a large diagnostic market. By providing economical quality testing on site, this system will produce widespread benefits to health care delivery.